1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device with integrated touch screen.
2. Discussion of the Related Art
Touch screens are a type of input device that is included in image display devices such as liquid crystal display (LCD) devices, field emission displays (FEDs), plasma display panels (PDPs), electroluminescent displays (ELDs), and electrophoretic displays (EPDs), and allows a user to input predetermined information by applying a pressure (i.e., pressing or touching) to a touch sensor of a touch screen while looking at the image display device.
The touch screen applied to display devices is categorized into an add-on type, an on-cell type, and an in-cell type depending on a structure thereof. The add-on type is a type in which a display device and a touch screen are separately manufactured, and the touch screen is adhered to an upper substrate of the display device. The on-cell type is a type in which a plurality of elements configuring a touch screen is provided at a surface of an upper glass substrate of a display device. The in-cell type is a type in which a touch screen is built into a display device, and thus, the display device is thinned, and a durability of the display device increases.
However, since the add-on type touch screen has a structure in which a finished touch screen is mounted on a display device, the add-on type touch screen is thick, and a brightness of the display device becomes dark, causing a reduction in visibility. Also, since the on-cell type touch screen has a structure in which a separate touch screen is provided at a top of a display device, the on-cell type touch screen is thinner than the add-on type touch screen, but due to a plurality of driving electrodes and a plurality of sensing electrodes configuring the touch screen and an insulating layer respectively connecting the plurality of driving electrodes and the plurality of sensing electrodes, a total thickness of the add-on type touch screen increases, and the number of processes increases, causing an increase in manufacturing cost.
The in-cell type touch screen can have an enhanced durability and a thin thickness, and thus can solve problems that occur in the add-on type touch screen and the on-cell type touch screen. The in-cell type touch screen is categorized into an optical touch screen and a capacitive touch screen.
The optical touch screen has a type in which a light sensing layer is formed at a thin film transistor (TFT) array substrate of a display device, a backlight unit emits light or infrared light, and light reflected from an object located at a touched position is sensed. However, the optical touch screen has a relatively stabilized drivability when an ambient environment is dark, but when the ambient environment is bright, light stronger than reflected light acts as noise. This is because an intensity of light reflected by an actual touch is very weak, and due to this, when the outside is bright even a little, an error can occur in sensing a touch. Especially, when an ambient environment is exposed to solar light, the optical touch screen cannot sense a touch depending on a case because the solar light is very strong.
The capacitive touch screen is categorized into a self-capacitive touch screen and a mutual capacitive touch screen. The mutual capacitive touch screen has a type in which a plurality of common electrodes are divided into a plurality of driving electrodes and a plurality of sensing electrodes, a mutual capacitance is generated between corresponding driving electrode and sensing electrode, and a touch is sensed by measuring a change amount of mutual capacitance caused by the touch.
However, in the mutual capacitive touch screen, a level of a mutual capacitance generated in sensing a touch is very low, but a parasitic capacitance between a gate line and a data line configuring a display device is very high, for which reason it is difficult to accurately detect a touched position. Also, since a plurality of touch driving lines for a touch driving and a plurality of touch sensing lines for a touch sensing should be formed on a common electrode, the mutual capacitance touch screen has a very complicated line structure.
Moreover, the mutual capacitive touch screen should separately scan the touch driving lines and the touch sensing lines so as to sense a touch, the total number of scans is a value which is obtained by multiplying the number of touch driving lines and the number of touch sensing lines. For example, a touch screen for small-size display devices includes ten touch driving lines and ten touch sensing lines, and thus needs to perform scan at least 100 or more times. The in-cell touch screen needs to perform a touch driving for a very short time, and thus can be applied to only display devices having a very small size.
For this reason, a display device with integrated self-capacitive and in-cell type touch screen is needed for solving the problems of the above-described types of touch screens.